InFO Coil Structure and Methods of Manufacturing Same

ABSTRACT

A method includes forming a coil over a carrier, encapsulating the coil in an encapsulating material, planarizing a top surface of the encapsulating material until the coil is exposed, forming at least one dielectric layer over the encapsulating material and the coil, and forming a plurality of redistribution lines extending into the at least one dielectric layer. The plurality of redistribution lines is electrically coupled to the coil.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.15/254,671, filed Sep. 1, 2016, and entitled “InFO Coil Structure andMethods of Manufacturing Same,” which claims the benefit of thefollowing provisionally filed U.S. patent application: Application Ser.No. 62/289,065, filed Jan. 29, 2016, and entitled “InFO Coil Structureand Methods of Manufacturing Same,” which applications are herebyincorporated herein by reference.

BACKGROUND

With the evolving of semiconductor technologies, semiconductorchips/dies are becoming increasingly smaller. In the meantime, morefunctions need to be integrated into the semiconductor dies.Accordingly, the semiconductor dies need to have increasingly greaternumbers of I/O pads packed into smaller areas, and the density of theI/O pads rises quickly over time. As a result, the packaging of thesemiconductor dies becomes more difficult, which adversely affects theyield of the packaging.

Conventional package technologies can be divided into two categories. Inthe first category, dies on a wafer are packaged before they are sawed.This packaging technology has some advantageous features, such as agreater throughput and a lower cost. Further, less underfill or moldingcompound is needed. However, this packaging technology also suffers fromdrawbacks. Since the sizes of the dies are becoming increasinglysmaller, and the respective packages can only be fan-in type packages,in which the I/O pads of each die are limited to the region directlyover the surface of the respective die. With the limited areas of thedies, the number of the I/O pads is limited due to the limitation of thepitch of the I/O pads. If the pitch of the pads is to be decreased,solder regions may bridge with each other, causing circuit failure.Additionally, under the fixed ball-size requirement, solder balls musthave a certain size, which in turn limits the number of solder ballsthat can be packed on the surface of a die.

In the other category of packaging, dies are sawed from wafers beforethey are packaged. An advantageous feature of this packaging technologyis the possibility of forming fan-out packages, which means the I/O padson a die can be redistributed to a greater area than the die, and hencethe number of I/O pads packed on the surfaces of the dies can beincreased. Another advantageous feature of this packaging technology isthat only “known-good-dies” are packaged, and defective dies arediscarded, and hence cost and effort are not wasted on the defectivedies.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 13 illustrate the cross-sectional views of intermediatestages in the formation of a package in accordance with someembodiments.

FIG. 14 illustrates a top view of a package including a coil, devicedies, and passive devices in accordance with some embodiments.

FIG. 15 illustrates a cross-sectional view of a package including a coiland no device die in accordance with some embodiments.

FIG. 16 illustrates a top view of a package including a coil and nodevice die in accordance with some embodiments.

FIG. 17 illustrates a cross-sectional view of a package including acoil, a device die, and an embedded passive device in accordance withsome embodiments.

FIG. 18 illustrates a process flow for forming a package in accordancewith some embodiments.

FIG. 19 illustrates a portion of the coil in accordance with someembodiments.

FIG. 20 illustrates a double-line coil in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A package including a coil penetrating through an encapsulating materialof the respective package and the method of forming the package areprovided in accordance with various exemplary embodiments. Theintermediate stages of forming the package are illustrated. Somevariations of some embodiments are discussed. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

FIGS. 1 through 13 illustrate the cross-sectional views and top views ofintermediate stages in the formation of some packages in accordance withsome embodiments of the present disclosure. The steps shown in FIG. 1through 13 are also schematically illustrated in the process flow 200shown in FIG. 18.

FIG. 1 illustrates carrier 20 and release layer 22 formed over carrier20. Carrier 20 may be a glass carrier, a ceramic carrier, or the like.Carrier 20 may have a round top-view shape, and may have a size of asilicon wafer. For example, carrier 20 may have an 8-inch diameter, a12-inch diameter, or the like. Release layer 22 may be formed of apolymer-based material (such as a Light To Heat Conversion (LTHC)material), which may be removed along with carrier 20 from the overlyingstructures that will be formed in subsequent steps. In accordance withsome embodiments of the present disclosure, release layer 22 is formedof an epoxy-based thermal-release material. In accordance with someembodiments of the present disclosure, release layer 22 is formed of anultra-violet (UV) glue. Release layer 22 may be dispensed as a liquidand cured. In accordance with alternative embodiments of the presentdisclosure, release layer 22 is a laminate film and is laminated ontocarrier 20. The top surface of release layer 22 is leveled and has ahigh degree of planarity.

In accordance with some embodiments of the present disclosure,dielectric layer 24 is formed over release layer 22. The respective stepis shown as step 202 in the process flow shown in FIG. 18. In the finalproduct, dielectric layer 24 may be used as a passivation layer toisolate the overlying metallic features from the adverse effect ofmoisture and other detrimental substances. Dielectric layer 24 may beformed of a polymer, which may also be a photo-sensitive material suchas polybenzoxazole (PBO), polyimide, benzocyclobutene (BCB), or thelike. In accordance with alternative embodiments of the presentdisclosure, dielectric layer 24 is formed of an inorganic material(s),which may be a nitride such as silicon nitride, an oxide such as siliconoxide, PhosphoSilicate Glass (PSG), BoroSilicate Glass (BSG),Boron-doped PhosphoSilicate Glass (BPSG), or the like. In accordancewith yet alternative embodiments of the present disclosure, nodielectric layer 24 is formed. Accordingly, dielectric layer 24 is shownwith dashed lines to indicate that it may or may not be formed.

FIGS. 2 and 3 illustrate the formation of conductive features 32, whichare referred to as through-conductors (or through-vias) hereinaftersince they penetrate the encapsulation material 52 (FIG. 6) that will beapplied in subsequent steps. Referring to FIG. 2, seed layer 26 isformed over dielectric layer 24, for example, through Physical VaporDeposition (PVD) or metal foil lamination. Seed layer 26 may be formedof copper, aluminum, titanium, or multi-layers thereof. In accordancewith some embodiments of the present disclosure, seed layer 26 includesa titanium layer (not shown) and a copper layer (not shown) over thetitanium layer. In accordance with alternative embodiments, seed layer26 includes a single copper layer.

Photo resist 28 is applied over seed layer 26 and is then patterned. Therespective step is also shown as step 202 in the process flow shown inFIG. 18. As a result, openings 30 are formed in photo resist 28, throughwhich some portions of seed layer 26 are exposed.

As shown in FIG. 2, through-conductors 32 are formed in openings 30through plating, which may be a suitable combination of electro platingand electro-less plating. The respective step is shown as step 204 inthe process flow shown in FIG. 18. Through-conductors 32 are plated onthe exposed portions of seed layer 26. Through-conductors 32 may includecopper, aluminum, tungsten, nickel, or alloys thereof. The top-viewpattern profile/shape of through-conductors 32 include, and are notlimited to, spirals, rings, rectangles, squares, circles, and the like,depending on the intended function of through-conductors 32. Althoughthrough-conductors 32 are illustrated as discrete features in thecross-sectional views throughout the description, they may be parts ofan integral conductor. The heights of through-conductors 32 aredetermined by the thickness of the subsequently placed device die 38(FIG. 6), with the eventual heights of through-conductors 32 beinggreater than or equal to the thickness of device die 38 in accordancewith various embodiments. The instant exemplary through-conductor 32 isconfigured to function as an inductor, and the heights ofthrough-conductors 32 may be determined in accordance with the desirableinductance of the inductor formed thereby. In accordance with someembodiments, middle width W2 measured at the mid-height is greater thanthe top width W1 and bottom width W3. In accordance with alternativeembodiments, top width W1 is greater than middle width W2, and middlewidth W2 is greater than bottom width W3.

After the plating of through-conductors 32, photo resist 28 is removed,and the resulting structure is shown in FIG. 3. The portions of seedlayer 26 (FIG. 2) that were previously covered by photo resist 28 areexposed. An etch step is then performed to remove the exposed portionsof seed layer 26, wherein the etching may be an anisotropic or isotropicetching. The portions of seed layer 26 that are overlapped bythrough-conductors 32, on the other hand, remain not etched. Throughoutthe description, the remaining underlying portions of seed layer 26 areconsidered as the bottom portions of through-conductors 32. When seedlayer 26 is formed of a material similar to or the same as that of therespective overlying through-conductors 32, seed layer 26 may be mergedwith through-conductors 32 with no distinguishable interfacetherebetween. Accordingly, seed layers 26 are not shown in subsequentdrawings. In accordance with alternative embodiments of the presentdisclosure, there exist distinguishable interfaces between seed layer 26and the overlying plated portions of through-conductors 32.

The top-view shape of through-conductors 32 is related to, and isdetermined by, their intended function. In accordance with someexemplary embodiments in which through-conductors 32 are used to form aninductor, the illustrated through-conductors 32 may be a part of coil33. In accordance with some embodiments, through-conductors 32 form aplurality of concentric rings (not shown), with the outer ringsencircling the inner rings. The rings have breaks to allow the outerrings to be connected to the inner rings through the subsequently formedredistribution lines. In accordance with some embodiment, as shown inFIGS. 14 and 16, through-conductors 32 are portions of an integratedspiral forming coil 33, which also includes outer rings encircling innerrings. Coil 33 has ports 34 at the opposite ends of coil 33.

FIG. 4 illustrates the placement of device die 38(s) over carrier 20 inaccordance with some embodiments of the present disclosure. Therespective step is shown as step 206 in the process flow shown in FIG.18. Device die 38 may be adhered to dielectric layer 24 throughDie-Attach Film (DAF) 40, which is an adhesive film. In accordance withsome embodiments of the present disclosure, device die 38 is an AC-DCconverter die, which is arranged to perform the function of receivingthe AC current from coil 33, and converting the AC current to a DCcurrent. The DC current is used to charge a battery (not shown), or todrive circuits of the respective product, in which the package includingcoil 33 is located. Device die 38 may also be a communication die, whichmay be Bluetooth Low-Energy (BLE) die. The BLE die 38 may have thefunction of communicating with a transmitter (not shown), for example,through Bluetooth technology. The transmitter and BLE die 38 maynegotiate the transmission of energy, for example, when the distancebetween the transmitter and coil 33 is small enough, and/or when thestored power in the battery is lower than a pre-determined thresholdlevel. The transmitter may than start transmitting energy, which may bein the form of magnetic field at a high frequency, for example, at about6.78 MHz. Coil 33 receives the energy, and feed the respective currentto AC-DC converter die 38. In accordance with some embodiments of thepresent disclosure, device die 38 represents both AC-DC converter dieand a BLE die.

Although one device die 38 is illustrated, more device dies may beplaced over dielectric layer 24. In accordance with some embodiments ofthe present disclosure, the formation of the package is at wafer-level.Accordingly, a plurality of device dies identical to device die 38 maybe placed on carrier 20, and is allocated as an array having a pluralityof rows and columns. Similarly, a plurality of coils identical to coil33 is formed simultaneously when coil 33 is formed.

Device die 38 may include semiconductor substrate 42, which may be asilicon substrate. Integrated circuit devices 44 are formed onsemiconductor substrate 42. Integrated circuit devices 44 may includeactive devices such as transistors and diodes and/or passive devicessuch as resistors, capacitors, inductors, or the like. Device die 38 mayinclude metal pillars 46 electrically coupled to integrated circuitdevices 44. Metal pillars 46 may be embedded in dielectric layer 48,which may be formed of PBO, polyimide, or BCB, for example. Passivationlayer 50 is also illustrated, wherein metal pillars 46 may extend intopassivation layer 50. Passivation layer 50 may include silicon nitride,silicon oxide, or multi-layers thereof.

Next, referring to FIG. 5, encapsulating material 52 isencapsulated/molded on device die 38. The respective step is shown asstep 208 in the process flow shown in FIG. 18. Encapsulating material 52fills the gaps between neighboring through-conductors 32 and the gapsbetween through-conductors 32 and device die 38. Encapsulating material52 may include a polymer-based material, and may include a moldingcompound, a molding underfill, an epoxy, and/or a resin. In accordancewith some embodiments of the present disclosure, encapsulating material52 includes an epoxy-based material and filler particles in theepoxy-based material. The filler particles may include, for example,Al₂O₃ particles, which may be spherical particles. The top surface ofencapsulating material 52 is higher than the top ends of metal pillar46.

In a subsequent step, as shown in FIG. 6, a planarization process suchas a Chemical Mechanical Polish (CMP) process or a grinding process isperformed to reduce the top surface of encapsulating material 52, untilthrough-conductors 32 and metal pillar 46 are exposed. The respectivestep is also shown as step 210 in the process flow shown in FIG. 18. Dueto the planarization, the top ends of through-conductors 32 aresubstantially level (coplanar) with the top surfaces of metal pillars46, and are substantially coplanar with the top surface of encapsulatingmaterial 52.

FIGS. 7 through 11 illustrate the formation of front-side RDLs and therespective dielectric layers. Referring to FIG. 7, dielectric layer 54is formed. The respective step is shown as step 212 in the process flowshown in FIG. 18. In accordance with some embodiments of the presentdisclosure, dielectric layer 54 is formed of a polymer such as PBO,polyimide, or the like. In accordance with alternative embodiments ofthe present disclosure, dielectric layer 54 is formed of an inorganicmaterial such as silicon nitride, silicon oxide, or the like. Openings55 are formed in dielectric layer 54 (for example, through exposure anddevelopment) to expose through-conductors 32 and metal pillars 46.Openings 55 may be formed through a photo lithography process.

Next, referring to FIG. 8, Redistribution Lines (RDLs) 58 are formed toconnect to metal pillars 46 and through-conductors 32. The respectivestep is shown as step 214 in the process flow shown in FIG. 18. RDLs 58may also interconnect metal pillars 46 and through-conductors 32. RDLs58 include metal traces (metal lines) over dielectric layer 54 and viasextending into dielectric layer 54. The vias in RDLs 58 are connected tothrough-conductors 32 and metal pillars 46. In accordance with someembodiments of the present disclosure, the formation of RDLs 58 includesforming a blanket copper seed layer, forming and patterning a mask layerover the blanket copper seed layer, performing a plating to form RDLs58, removing the mask layer, and etch the portions of the blanket copperseed layer not covered by RDLs 58. RDLs 58 may be formed of a metal or ametal alloy including aluminum, copper, tungsten, and/or alloys thereof.

Referring to FIG. 9, in accordance with some embodiments, dielectriclayer 60 is formed over the structure shown in FIG. 8, followed by theformation of openings 62 in dielectric layer 60. Some portions of RDLs58 are thus exposed. The respective step is shown as step 216 in theprocess flow shown in FIG. 18. Dielectric layer 60 may be formed using amaterial selected from the same candidate materials for formingdielectric layer 54.

Next, as shown in FIG. 10, RDLs 64 are formed in dielectric layer 60.The respective step is also shown as step 216 in the process flow shownin FIG. 18. In accordance with some embodiments of the presentdisclosure, the formation of RDLs 64 includes forming a blanket copperseed layer, forming and patterning a mask layer over the blanket copperseed layer, performing a plating to form RDLs 64, removing the masklayer, and etching the portions of the blanket copper seed layer notcovered by RDLs 64. RDLs 64 may also be formed of a metal or a metalalloy including aluminum, copper, tungsten, and/or alloys thereof. It isappreciated that although in the illustrated exemplary embodiments, twolayers of RDLs (58 and 64) are formed, the RDLs may have any number oflayers such as one layer or more than two layers.

FIGS. 11 and 12 illustrate the formation of dielectric layer 66 andelectrical connectors 68 in accordance with some exemplary embodiments.The respective step is shown as step 218 in the process flow shown inFIG. 18. Referring to FIG. 11, dielectric layer 66 is formed, forexample, using PBO, polyimide, or BCB. Openings 59 are formed indielectric layer 66 to expose the underlying metal pads, which are partsof RDLs 64. In accordance with some embodiment, Under-Bump Metallurgies(UBMs, not shown) are formed to extend into opening 59 in dielectriclayer 66.

Electrical connectors 68 are then formed, as shown in FIG. 12. Theformation of electrical connectors 68 may include placing solder ballson the exposed portions of the UBMs, and then reflowing the solderballs. In accordance with alternative embodiments of the presentdisclosure, the formation of electrical connectors 68 includesperforming a plating step to form solder regions over the exposed metalpads in RDLs 64, and then reflowing the solder regions. Electricalconnectors 68 may also include metal pillars, or metal pillars andsolder caps, which may also be formed through plating. Throughout thedescription, the structure including dielectric layer 24 and theoverlying structure in combination is referred to as package 100, whichis a composite wafer including a plurality of device dies 38.

Next, package 100 is de-bonded from carrier 20, for example, byprojecting a UV light or a laser beam on release layer 22, so thatrelease layer 22 decomposes under the heat of the UV light or the laserbeam. Package 100 is thus de-bonded from carrier 20. The respective stepis shown as step 220 in the process flow shown in FIG. 18. In accordancewith some embodiments of the present disclosure, in the resultantpackage 100, dielectric layer 24 remains as a bottom part of package100, and protects through-conductors 32. Dielectric layer 24 may be ablanket layer with no through-opening therein. In accordance withalternative embodiments, dielectric layer 24 is not formed, and thebottom surfaces of encapsulating material 52 and through-conductors 32are exposed after the de-bonding. A backside grinding may (or may not)be performed to remove DAF 40, if it is used, so that the bottomsurfaces of through-conductors 32 are coplanar with the bottom surfaceof device die 38 and the bottom surface of encapsulating material 52.The bottom surface of device die 38 may also be the bottom surface ofsemiconductor substrate 42.

Package 100 is then singulated (sawed) into a plurality of packages 100′that is identical to each other. The respective step is shown as step222 in the process flow shown in FIG. 18. FIG. 13 illustrates anexemplary package 100′. FIG. 13 also illustrates the bonding of package100′ to package component 110, for example, through electricalconnectors 68. Package component 110 may be a Printed Circuit Board(PCB), an interposer, a package substrate, a device package, or thelike. In accordance with alternative embodiments, package 100′ iselectrically connected to a flex PCB (not shown, similar to flex PCB 72in FIG. 17), which may overlap coil 33, or may be connected sideways.

FIG. 14 illustrates a top view of the package 100′ shown in FIG. 13,wherein the cross-sectional view shown in FIG. 13 is obtained from theplane containing line 13-13 in FIG. 14. In accordance with someembodiments of the present disclosure, ports 34 of coil 33 are connectedto device die 38 (denoted as 38A), which may be an AC-DC converter die.A BLE die, which is denoted as 38B, is also disposed in package 100′ inaccordance with some embodiments.

Passive devices 56 are also included in package 100′. Passive devices 56may be Integrated Passive Devices (IPDs), which are formed onsemiconductor substrates in the respective chips. Throughout thedescription, an IPD may be a single-device chip, which may include asingle passive device such as an inductor, a capacitor, a resistor, orthe like, with no other passive devices and active devices in therespective chip. Furthermore, in accordance with some embodiments, thereare no active devices such as transistors and diodes in the IPDs.

In accordance with some embodiments of the present disclosure, passivedevices 56 include Surface Mount Devices (SMDs, denoted as 56A) bondedonto RDLs 64 or solder regions 68, as shown in FIG. 17. In accordancewith alternative embodiments, passive devices 56 include embeddedpassive devices 56B, which may be placed on carrier 20 before theencapsulation step as shown in FIG. 5. The respective passive devices56B are also shown in FIG. 17, wherein the notation 38/56B indicatesthat the respective component(s) may be device die 38, passive device(such as an IPD) 56B, or may include both a device die and a passivedevice that are separate from each other. Similarly, the passivedevice(s) 56B encapsulated in encapsulating material 52 may have theirrespective surface conductive features (similar to 46) exposed in theplanarization step as shown in FIG. 6. Accordingly, passive devices 56Bare electrically coupled to other devices through RDLs 58 and/or 64. Inaccordance with alternative embodiments, there is no passive deviceencapsulated in encapsulating material 52.

Referring back to FIG. 14, in accordance with some embodiments of thepresent disclosure, the portion of encapsulating material 52 encircledby coil 33 does not have any conductive material such as through-viastherein. Accordingly, the portion of encapsulating material 52 encircledby coil 33 also may not have any passive or active device therein.

FIG. 14 also illustrates bond pads 70, which are used for connecting thecomponents in package 100′ to a flex PCB 72 (not shown in FIG. 14, referto FIG. 17) in accordance with some exemplary embodiments. Bond pads 70are electrically coupled to device die 38A, device die 38B, and/orpassive devices 56 through RDLs 58 and 64 (FIG. 13).

FIG. 15 illustrates a cross-sectional view of a package in accordancewith some embodiments of the present disclosure. These embodiments aresimilar to the embodiments in FIGS. 13 and 14, except no device die(having active devices) and passive device are located in package 100′.Alternatively stated, in accordance with some embodiments of the presentdisclosure, all conductive features inside encapsulating material 52 arethe parts of coil 33. Accordingly, package 100′ includes coil 33 and therespective electrical connection structures, but no additional devices,and package 100′ is a discrete coil.

FIG. 16 illustrates a top view of package 100′ in accordance with someembodiments of the present disclosure, wherein the cross-sectional viewshown in FIG. 15 is obtained from the plane containing line 15-15 inFIG. 16. As shown in FIG. 16, coil 33 extends to proximal all edges ofpackage 100′, except some process margin is left to ensure an adequate,but not excessive, amount of encapsulating material 52 is on the outersides of coil 33. As a result, the footprint size (the top-view area) ofpackage 100′ is minimized. The portions of encapsulating material 52 onthe outer sides of coil 33 prevent coil 33 from being exposed to openair. As shown in FIG. 16, there is no active and passive device insideor outside coil 33 and in encapsulating material 52.

FIG. 17 illustrates a cross-sectional view of package 100′ in accordancewith some embodiments. As shown in FIG. 17, passive device 56A is overdielectric layers 54, 60, and 66, and may be bonded to metal pads 64through solder regions 68. Device die 38 and/or passive device 56B areembedded in encapsulating material 52. Flex PCB 72 is connected to metalpads 70, for example, through solder regions 68. Furthermore, passivedevice 56A may directly overlap passive device 56B to better use thepackage area and to reduce the footprint of the resulting package.

In accordance with some embodiments, ferrite material 74 is attached todielectric layer 66 through, for example, adhesive film 76. Ferritematerial 74 may include manganese-zinc, nickel-zinc, or the like.Ferrite material 74 has comparatively low losses at high frequencies,and is used to increase the inductance of inductor 33. Ferrite material74 overlaps coil 33, and the edges of ferrite material 74 may besubstantially co-terminus with the edges of coil 33.

FIG. 19 illustrates an amplified view of portion 82 of package 100′ inFIGS. 14 and 16, wherein two through-conductors 32 are illustrated as anexample. To reduce stress, through-conductors 32 may have roundedcorners. For example, the radius R1 of through conductors may be in therange between about W1/2 and 2W1/3.

To enhance the efficiency, the outer rings of coil 33 may have widthsgreater than or equal to the widths of the inner rings in accordancewith some embodiments. For example, referring to FIGS. 14 and 16, widthW1A, which may be the width of the outmost ring, may be equal to orgreater than width W1B of the innermost ring. Ratio W1B/W1A may be inthe range between about ½ and about ⅔. Furthermore, from outer rings tothe inner rings, the widths of through-conductors 32 may be increasinglyreduced or periodically reduced every several rings.

FIG. 20 illustrates package 100′ including a double-line coil 33 inaccordance with some embodiments. For a clearer view, RDLs 58 and 64(FIG. 14) that connect the ends of coil 33 to device die 38A are notillustrated in FIG. 20. The coil 33 in FIG. 20 may be essentially thesame as the corresponding coil in FIG. 14 or FIG. 16, except that coil33, instead of having a single through-conductor 32 coiling, has twothrough-conductors 32A and 32B coiling in parallel. Through-conductors32A and 32B are parallel to each other, and are in combination used likea single conductor to form coil. In order to distinguishthrough-conductors 32A from 32B, so that their layouts can be clearlyseen, through-conductors 32A and 32B are shown using different patterns.

As shown in FIG. 20, each of through-conductors 32A and 32B by itselfforms a coil. The ends of through-conductors 32A and 32B areinterconnected through connectors 74A and 74B. Each of connectors 74Aand 74B may be a through-via formed simultaneously whenthrough-conductors 32A and 32B are formed, or may be a part of RDLs 58and 64. Connectors 74A and 74B may also include both thethrough-conductor portion and the RDL portion. In accordance with someembodiments, through-conductors 32A and 32B are only connected at theirends, but not in the middle, as shown in FIG. 20. In accordance withalternative embodiments, additional connectors similar to connectors 74Aand 74B may be formed periodically to interconnect the middle portionsof through-conductor 32A to the respective middle portions ofthrough-conductor 32A. For example, each straight portion ofthrough-conductors 32A and 32B may include one or more interconnector.The coil 33 as shown in FIGS. 19 and 20 may be combined with allembodiments as illustrated.

As a result of the interconnection of through-conductors 32A and 32B,through-conductors 32A and 32B in combination form the coil. Whenoperated at a high frequency, for example, several megahertz or higher,coil 33 in FIG. 20 has the performance comparable to, and sometimesbetter than, bulk coil 33 as shown in FIGS. 14 and 16. This may becaused by skin effect. Furthermore, with through-conductors 32A and 32Bbeing narrower compared to a bulk coil since it is equivalent toremoving a middle part of through-conductor 32 as shown in FIGS. 14 and16, the pattern loading effect in the plating of through-conductors 32Aand 32B is reduced.

The embodiments of the present disclosure have some advantageousfeatures. Coil 33 is formed in an encapsulating material, and hence theheight of coil 33 may have a great value. The inductance of coil 33 isthus high. Coil 33 may also be formed using the same packaging processfor packaging device dies, and may be integrated within the same packageas device dies and passive devices, resulting in the reduction offootprint and the manufacturing cost of packages.

In accordance with some embodiments of the present disclosure, a methodincludes forming a coil over a carrier, encapsulating the coil in anencapsulating material, planarizing a top surface of the encapsulatingmaterial until the coil is exposed, forming at least one dielectriclayer over the encapsulating material and the coil, and forming aplurality of redistribution lines extending into the at least onedielectric layer. The plurality of redistribution lines is electricallycoupled to the coil.

In accordance with some embodiments of the present disclosure, a methodincludes forming a coil over a carrier, wherein in a top view of thecoil, the coil comprises outer rings encircling inner rings,encapsulating the coil in an encapsulating material, grinding theencapsulating material, wherein top surfaces of the outer rings and theinner rings of the coil are exposed as a result of the grinding, forminga dielectric layer over the encapsulating material and the coil, andpatterning the dielectric layer to form a first opening and a secondopening. A first end and a second end of the coil are exposed throughthe first opening and the second opening, respectively. The methodfurther includes forming electrical connections to electrically coupleto the coil.

In accordance with some embodiments of the present disclosure, astructure includes a coil having outer rings encircling inner rings, andan encapsulating material encapsulating the coil therein. Theencapsulating material has a top surface coplanar with top surfaces ofthe outer rings and top surfaces of the inner rings. The structurefurther includes a dielectric layer over and contacting theencapsulating material and the coil, a first opening and a secondopening in the dielectric layer, and a first and a second redistributionline extending into the first opening and the second opening,respectively, to contact opposite ends of the coil.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A package comprising: a coil comprising innerrings and outer rings encircling the inner rings; an encapsulatingmaterial encapsulating the coil therein, wherein the encapsulatingmaterial has a top surface level with top surfaces of the outer ringsand top surfaces of the inner rings; a dielectric layer over andcontacting the encapsulating material and the coil; and a first and asecond redistribution line extending into the dielectric layer tocontact opposite ends of the coil.
 2. The package of claim 1, wherein abottom surface of the encapsulating material is further level with abottom surface of the outer rings and the inner rings of the coil. 3.The package of claim 1, wherein the encapsulating material encircles anentirety of a region encircled by the coil.
 4. The package of claim 1,wherein the coil is a double-line coil comprising two conductors inparallel, and first ends of the two conductors are interconnected, andsecond ends of the two conductors are interconnected, with the firstends and the second ends being opposite ends of the two conductors. 5.The package of claim 1 further comprising a device die encapsulated inthe encapsulating material, wherein electrical connectors of the devicedie have top surfaces level with a top surface of the encapsulatingmaterial.
 6. The package of claim 5, wherein a bottom surface of thedevice die, bottom surfaces of the outer rings and the inner rings, anda bottom surface of the encapsulating material are level with eachother.
 7. The package of claim 1 further comprising a passive devicedie, wherein conductive features of the passive device die have topsurfaces level with a top surface of the encapsulating material.
 8. Thepackage of claim 1 being free from device dies that are embedded in theencapsulating material.
 9. The package of claim 8 further comprising: apackage component comprising a first electrical connector and a secondelectrical connector; and a first solder region and a second solderregion, wherein the first solder region electrically couples a first endof the coil to the first electrical connector, and the second solderregion electrically couples to the second electrical connector.
 10. Apackage comprising: a coil forming a spiral, wherein the coil has afirst end and a second end; a device die comprising a first electricalconnector and a second electrical connector; a molding compound, withthe coil and the device die being encapsulated in the molding compound;a dielectric layer, wherein a bottom surface of the dielectric layer isin contact with a top surface of the device die, a top surface of thecoil, and a top surface of the molding compound; a first redistributionline connecting the first end of the coil to the first electricalconnector; and a second redistribution line connecting the second end ofthe coil to the second electrical connector, wherein the firstredistribution line and the second redistribution line comprise portionsextending into the dielectric layer.
 11. The package of claim 10,wherein the device die is an AC-DC converter die configured to convertan energy collected by the coil into a DC current.
 12. The package ofclaim 10, wherein the coil comprises a plurality of rings, with outerones of the plurality of rings encircling respective inner ones of theplurality of rings, wherein each of the plurality of rings penetratesthrough the molding compound.
 13. The package of claim 12, wherein topsurfaces of the plurality of rings are level with a top surface of themolding compound, and bottom surfaces of the plurality of rings arelevel with a bottom surface of the molding compound.
 14. The package ofclaim 10, further comprising an adhesive film underlying the device die,wherein a bottom surface of the adhesive film is level with bottomsurfaces of the coil and a bottom surface of the molding compound.
 15. Apackage comprising: a coil comprising a first end and a second end,wherein the first end and the second end are opposite ends of the coil;a device die comprising a first metal pillar and a second metal pillar;an encapsulant encapsulating the device die and the coil therein; afirst dielectric layer comprising a bottom surface contacting a topsurface of the coil, a top surface of the device die, and a top surfaceof the encapsulant; a second dielectric layer comprising a top surfacecontacting a bottom surface of the coil and a bottom surface of theencapsulant; and a plurality of redistribution lines comprising portionsextending into the first dielectric layer, wherein the first end and thesecond end of the coil are electrically coupled to the first metalpillar and the second metal pillar, respectively, through the pluralityof redistribution lines.
 16. The package of claim 15, wherein theencapsulant comprises an epoxy-based material and filler particles mixedin the epoxy-based material.
 17. The package of claim 15 furthercomprising an adhesive film between the device die and the seconddielectric layer, wherein a bottom surface of the adhesive film contactsthe top surface of the second dielectric layer.
 18. The package of claim15, wherein the device die comprises an AC-DC converter.
 19. The packageof claim 18 further comprising a Bluetooth low-energy die encapsulatedin the encapsulant.
 20. The package of claim 15, wherein the coil has aspiral shape.